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Biunnilium
Biunnilium, Bun, is the temporary name for element 210. NUCLEAR What follows is based on a first-order, liquid-drop assessment of where the outer boundary of the nuclear world is. Assume cautious values for how many neutrons a nucleus with 210 protons can bind (high neutron dripline) and how few it can have before it fissions immediately regardless of how much the structure it can develop stabilizes it (low must-fission curve). Assume, too, that anything that lasts long enough so that protons and neutrons can be treated as particles rather than collections of quarks (is causal) might be a nucleus. Under these conditions, Bun isotopes are theoretically possible between Bun 613 and Bun 934 (see "The Final Element", this wiki). Bun 613 through Bun 739 are expected to decay by beta emission if they don’t fission quickly. Above that value of A, the confident neutron dripline, drops may decay by neutron emission before they can fission. (Structural correction does not affect neutron emission.) Isotopes lighter than Bun 644 need more than twice the structural correction energy needed to prevent fission in worst-case nuclei in the A = 480 region(1). Predicting whether or not the structure a nuclear drop can develop will allow it to survive for the 10^-14 sec required for it to bind an electron and so become an atomic nucleus is not usually possible at this time. Neutron shell closures have been predicted at N = 644, and 524(2). There is a small chance the former allows some nuclei in the vicinity of Bun 854; it requires only 1.5 MeV structural correction, but is 16% above the confident dripline. The isotope Bun 734 requires 6.0 MeV of structural correction; however a proton shell closure predicted at Z = 210(2) will confer additional stability. That, plus the fact that Bun 734 lies below the confident dripline, means some isotopes between Bun 724 and Bun 739 are not merely possible, but likely. Isotopes up to Bun 859 also have some probability of existing. Bun 643 and lighter are implausible, while Bun 860 and heavier are highly unlikely. The doubly-magic nuclide Bun 734 anchors the outermost realistic island of stability. ATOMIC Electron structure of Bun has not been studied closely, but it is likely to differ significantly from the conventional orbitals found in lower-Z nuclei. While only the innermost electrons would be qualitatively different, other electrons are likely to be quantitatively different from those in lower-Z atoms. Bun is also large enough that nuclear shape may have an effect on electron structure, which might cause different isotopes of Bun to be chemically different. (Which means it is no longer an element in the chemical sense.) Predictions of atomic or chemical properties of Bun are risky. FORMATION Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. It is probably impossible for lighter isotopes to form in this way. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Bun 724 to Bun 739 band. Quantities amount to a few atoms per star at best. REFERENCES 1. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 2. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. (12-05-19)